It is well known to cut either metals or nonmetals by a laser beam focused on the surface of the material and moved along the surface to melt away the material in the path of the laser. It is further known to augment this process by employing a jet of gas to blow away the molten material to assure that it is removed from the cut before it resolidifies. The gas may include oxygen or other gases which react with the material to assist in the operation.
The apparatus for lasser cutting with gas assist generally comprises a laser, a housing containing a reservoir coupled to a source of pressurized gas, a nozzle having a round aperture for emitting the gas against the material being cut, and focusing optics in the housing to aim the laser beam through the nozzle aperture and onto the surface of the material. Typically the lasser beam is concentric with the nozzle aperture so that the gas impacts on the spot being heated by the laser. A variant of this is disclosed in the U.S. Pat. No. 4,871,897 to Nielsen which suggests displacing the laser beam from the nozzle center in the direction of cutting movement so that the gas impacts on material which has already been melted. The nozzle opening may have a circular, elliptical or other shape. To accomodate cutting along a curved path, the nozzle rotates to keep the laser beam and the nozzle center aligned in the direction of cutting.
The speed of the cutting operation is dependent on the laser power but is limited by the interaction time (of the laser energy and the gas with the workpiece) required to melt through the material thickness. Even if the lasser energy level and the gas flow are increased, there is a minimum time required to cut through the workpiece due to the time phased cutting cycle. This cycle includes heating the workpiece to the melting point using radiant and exothermic energy, and the blowing the melted material out the back side of the workpiece. As a result, circular concentric focus spots and nozzle openings must be moved slowly enough to expose the material to the gas and radiation for a minimum length of time. It is desirable to overcome the speed limitation to make the process more economical and thus widen its field of application.